1. Field of the Invention
The present invention relates to a control method for acquiring signals from photoelectric conversion elements and obtaining an image, an imaging apparatus that performs such control, and a radiation imaging system.
2. Description of the Related Art
In recent years, in a field of a digital X-ray imaging apparatus, in place of an image intensifier, an image sensor having a large area in which photoelectric conversion elements are arranged in a matrix has become popular. Compared to the image intensifier, the image sensor can improve resolution of an image, reduce distortion of an image, and downsize a volume of the imaging apparatus. Image sensors include image sensors of an amorphous silicon type, a charge coupled device (CCD) type, and a complementary metal-oxide semiconductor (CMOS) type.
In the above described image sensor, since noise enters elements included in a circuit, signals need to be extracted corresponding to an amount of received light while the noise is being removed. According to U.S. Pat. No. 6,950,132, a circuit is provided that applies reset potential to a light signal line and a noise signal line disposed between a circuit holding outputs of image pixels and a differential amplifier. By clamping a reset state generated by the reset potential at a subsequent stage of the differential amplifier, the noise of the differential amplifier can be removed.
In a period when the signals are not read from the pixels, a column signal line connected to a scanning line and a row signal line serving as an output line of an image circuit are set to a floating state. Since the signal lines on an element substrate have a certain capacity, the noise is superimposed on the signal lines, which results in an adverse effect on image quality.
Further, since the noise varies within a certain range over time, each of the images includes a different amount of noise superimposed thereon. According to the technique described in U.S. Pat. No. 6,950,132, in which a circuit for applying the reset potential to the signal line and a clamp circuit disposed at a subsequent stage of the signal line are separately required, a circuit structure becomes complicated.